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Thread: Earthing Transformer

  1. #1
    Join Date
    Mar 2008
    Location
    Alabama
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    17

    Earthing Transformer

    We have a 11kv buss to run our thruster drives. We have Earthing transformers in several locations after tie breakers. The transformers step down to 220 with a 40amp fuse on the primary side. The secondary taps of the transformers tie to ground through resistors to a common point. I am asking for some expertise in understanding the true function of this setup. I am thinking to dissipate residual voltage on large motors after a breaker has been opened.

    Thanks for any help.

  2. #2
    Join Date
    Mar 2005
    Location
    California
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    1,973
    Check out 250.24(B)(4) & 250.36
    Last edited by tryinghard; 03-11-11 at 09:30 AM.

  3. #3
    Join Date
    Mar 2008
    Location
    Alabama
    Posts
    17

    thanks

    Thanks for the Code book info. I am in Brazil working offshore and my code book is back home. I am really looking for technical info. Thanks Again. If you could post a short on what the code book says that would be nice also.

  4. #4
    Join Date
    Mar 2008
    Location
    Alabama
    Posts
    17

    ?

    thanks
    Last edited by SC1959; 03-11-11 at 09:11 PM.

  5. #5
    Join Date
    Mar 2005
    Location
    California
    Posts
    1,973
    250.24(C)(4) High Impedance. The grounded conductor on a high-impedance grounded neutral system shall be grounded in accordance with 250.36

    250.36 High-Impedance Grounded Neutral Systems. High-impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits the ground-fault current to a low value shall be permitted for 3-phase ac systems of 480 volts to 1000 volts if all the following conditions are met:
    • (1) The conditions of maintenance and supervision ensure that only qualified persons service the installation.
      (2) Ground detectors are installed on the system.
      (3) Line-to-neutral loads are not served.

    High-impedance grounded neutral systems shall comply with the provisions of 250.36(A) through (G)
    • (A) Grounded Impedance Location…
      (B) Grounded System Conductor…
      (C) System Grounding Connection…
      (D) Neutral Point to Grounding Impedance Conductor Routing…
      (E) Equipment Bonding Jumper…
      (F) Grounding Electrode Conductor Location…
      (G) Equipment Bonding Jumper Size…

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